The present invention relates to an automobile evaporative emission control device for controlling the emission to the atmosphere of fuel vapors from an internal combustion engine fuel system wherein the emission arises from the evaporation of the fuel.
It has generally been recognized by those skilled in the art that a major cause of air pollution so far as automobiles are concerned arises not only from the emission of combustion products through the exhaust system, but also from the fuel vapors emitted due to evaporation of the fuel. The U.S. Pat. No. 3,540,423 to Edward D. Tolles III, patented on Nov. 17, 1970, describes the possibility of air pollution resulting from the emission of the fuel vapors in automobiles and the importance of prevention of such fuel vapor emission. To this end, the E. D. Tolles' patent discloses an automobile evaporative emission control device which comprises an air filter or cleaner housing mounted on an intake manifold, leading to an engine combustion chamber or chambers through a carburetor; a gating valve operatively disposed in a primary air intake passage communicated to the atmosphere on one hand and, on the other hand, to the intake manifold through an annular adsorbent bed housed in the air cleaner housing, the gating valve being normally urged to a closed position by a biasing spring, but capable of being brought to an opened position in response to the negative pressure developed in the intake manifold at a position proximate to the throttle valve in the carburetor, the annular adsorbent bed defining a secondary air intake passage which extends through the central hollow of the annular adsorbent bed and is in communication with the intake manifold upstream of the carburetor and downstream of the adsorbent bed; and a pressure responsive two-way valve assembly so designed as to operate in such a manner that, when the engine is not operating or is operating at a low air consumption with no primary air introduced through the gating valve, a fluid circuit between the carburetor fuel bowl to the upstream side of the adsorbent bed can be established and, when increased engine air consumption is attained with the primary air introduced through the gating valve together with the secondary air, an alternative fluid circuit can be established between the carburetor fuel bowl and the intake manifold upstream of the throttle valve.
The pressure responsive two-way valve assembly employed in the Tolles' patent is comprised of a pressure responsive diaphragm valve and a two-way valve operatively coupled therewith while the gating valve is employed in the form of a butterfly valve.
The Tolles' patent also discloses the communication between the fuel tank and the first mentioned fluid circuit downstream of the pressure responsive two-way valve assembly, that is, between the fuel tank and a portion of the first mentioned fluid circuit which is between the pressure responsive two-way valve assembly and the annular adsorbent bed for withdrawing fuel vapors from the fuel tank to the adsorbent bed together with fuel vapors from the carburetor fuel bowl when the pressure responsive two-way valve assembly is held in position to establish the first mentioned fluid circuit.
The Japanese Utility Model Publication No. 47-10003 published on Apr. 14, 1972, discloses a similar automobile evaporative emission control device which comprises an air cleaner housing mounted on an intake manifold leading to an engine combustion chamber or chambers through a carburetor, the air cleaner housing having an air intake duct outwardly extending therefrom, said air intake duct including a gating valve, in the form of a butterfly valve, disposed therein for rotation between closed and opened positions and operatively coupled to a diaphragm valve. The diaphragm valve has a diaphragm member coupled to the gating valve through a connecting rod and being displaceable between a first position, in which the gating valve is held in the closed position, and a second position in which the gating valve is held in the opened position. This diaphragm valve is operatively associated with the intake manifold in such a manner that, when the engine is not operating or is operating at a low air consumption, the diaphragm is displaced to the first position with the gating valve consequently held in the closed position and, when the engine is operating at an increased air consumption, the diaphragm is displaced to the second position with the gating valve consequently held in the opened position for the introduction of air into the intake manifold through the air cleaner housing. For recovering fuel vapors from both of the intake manifold and the fuel tank, the emission control device disclosed in this Japanese Utility Model Publication further comprises a filter housing having two inlet ports, respectively communicated to the fuel tank and a portion of the air duct between the air cleaner housing and the gating valve whereby, while fuel vapors within the fuel tank are always introduced into the filter housing prior to the discharge thereof to the atmosphere irrespective of the engine operating condition, fuel vapors occurring in the intake manifold are introduced into the filter housing when and so long as the gating valve is held in the closed position. For operating the diaphragm valve, the negative pressure is drawn from the intake manifold from a position corresponding to a venturi section of the carburetor.
In the arrangement disclosed in the above mentioned Japanese Utility Model Publication, since the absolute value of the negative pressure developed in the venturi section of the carburetor is relatively small, the gating valve cannot be accurately and precisely operated between the closed and opened position and, more particularly, the gating valve can not readily be brought to the opened position during the engine idling condition.
However, the Japanese Utility Model Laid-open Publication No. 52-10211, laid open to public inspection on Jan. 24, 1977, discloses the use of an electromagnetic valve, instead of the butterfly valve employed in the above mentioned Japanese Utility Model Publication, for opening the air duct when and so long as the automobile ignition switch is turned on.
However, it has been found that the use of the electromagnetic valve requires consumption of an electric power, but also the electromagnetic valve itself is expensive.
Although less pertinent to the present invention than the prior art references hereinbefore discussed, the U.S. Pat. No. 3,683,878 to Joe E. Rogers, patented on Aug. 15, 1972, discloses the use of a gating valve of a type normally biased by a leaf spring to allow the passage of the primary air into the filter housing and then into the intake manifold while blocking the flow of air or fuel vapor in the opposite direction from the filter housing to the atmosphere. This type of gating valve may be considered a reed valve.
In any event, the conventional evaporative emission control devices particularly disclosed in the Tolles' patent and the Japanese Utility Model Publication involve a common disadvantage. As is well known to those skilled in the art, when the engine, which has been decelerated or has been operated at a relatively low velocity starts its acceleration to attain a relatively high velocity, the throttle valve is generally fully opened temporarily and the rate of flow of the primary air into the intake manifold by way of the air cleaner housing is consequently increased with the negative pressure present in the intake manifold at a position proximate to the throttle valve being reduced. In view of this, in the conventional evaporative emission control devices referred to above, the gating valve appears to be substantially closed during this transit period in which the engine is accelerated, to such an extent that the amount of the primary air to be introduced into the intake manifold tends to become short of the amount required during the substantially full opening of the throttle valve, the consequence of which is that the response of the engine to the acceleration is adversely affected.